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Five Reasons to Love Vampire Bats

They have a scary name. But vampire bats pose a small risk to people, and an infinitesimal one to Americans. They're some of the most amazing creatures on the planet, and they could even hold secrets to new drugs and treatments for humans.

Earlier this month, the Centers for Disease Control and Prevention announced that a 19-year-old man died of rabies he had contracted from a vampire bat, making it the first documented case of rabies from this animal in the U.S. Actually, the migrant worker was bitten in his native Mexico, about 10 days before traveling to a sugar cane plantation in Louisiana to work, according to a CDC investigation following his death on August 21, 2010.
Subsequent news reports suggested that vampire bats are moving into the U.S. and constitute a significant threat to people. In fact, neither statement is true. And while vampire bats aren't to be taken lightly, there are plenty of reasons to admire them, including complex social networks, deadly hunting skills and naturally producing chemicals that could become valuable human drugs. Not bad for a bunch of blood suckers.

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They Could Be the Key to New Drugs

Earlier this month, the Centers for Disease Control and Prevention announced that a 19-year-old man died of rabies he had contracted from a vampire bat, making it the first documented case of rabies from this animal in the U.S. Actually, the migrant worker was bitten in his native Mexico, about 10 days before traveling to a sugar cane plantation in Louisiana to work, according to a CDC investigation following his death on August 21, 2010.

Subsequent news reports suggested that vampire bats are moving into the U.S. and constitute a significant threat to people. In fact, neither statement is true. And while vampire bats aren't to be taken lightly, there are plenty of reasons to admire them, including complex social networks, deadly hunting skills and naturally producing chemicals that could become valuable human drugs. Not bad for a bunch of blood suckers.

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They Don't Live in the United States—Yet

Let's just get this one out of the way. Vampire bats are amazing creatures, for reasons to be explained soon. And they are responsible for very few rabies cases in humans.

But as last week's case reinforces, vampire bats can indeed carry the disease, and they aren't to be taken lightly. So perhaps they're best admired from afar, and Americans get to do just that. Bill Schutt, a research associate at the American Museum of Natural History who has studied the animals extensively, says vampire bats don't live in the U.S. and aren't expected to any time soon. While the CDC report correctly states that the animal's range could be expanding, Schutt says, he disagrees with the suggestions that this will happen in the near future. The research the report cites relies on a theoretical model of vampire bat habitat that hasn't been thoroughly tested, he says, and pertains to climate changes predicted to take place over many decades.

For now, the northernmost extent of vampire bats' range is about 100 miles south of Texas, though most live much farther south, says Shahroukh Mistry, a bat researcher at Butte College in California. Their range extends southward through Central and South America and two Caribbean islands. The unlucky rabies victim who died in Louisiana was bitten in Michoacán, Mexico—about 500 miles southwest of Texas.

(A note about rabies: Worldwide, rabid dogs are by far the largest source of the virus, especially in developing countries. In the U.S., thanks to the aggressive vaccination of pets such as dogs, non–vampire bats have become the largest source of rabies. But only a total of 32 cases have been reported in the past decade, and one-quarter of those were from exposure abroad. Daniel Streicker, a doctoral student at the University of Georgia who studies rabies in bats, says that most people who get rabies from (non–vampire) bats pick up sick animals lying on the ground. That's a bad idea, he says, and anybody who may have been bitten by a bat should seek medical attention. If treated early, rabies can be cured. But once symptoms appear, it's too late.)

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They Have a Rare Combination of Talents

Of the 1240 species of bats (which are the second largest group of mammals), only three of them are vampires, Schutt says. The common vampire bat, Desmodus Rotundus, feeds mostly on large mammals such as horses and cattle, although it occasionally bites people, especially if they are sleeping outdoors or in a room with open windows. The other two species are less common and mostly feed on birds.

Since the bats survive entirely on blood, they have developed a variety of unique traits. Unlike other bats, they are very quick and agile on the ground, able to run and jump like giant spiders, leaping up to 3 feet in the air without flying. But almost all other bats cannot walk like this; they've lost the ability. Recent research suggests that vampire bats developed their own way of walking, independent from any other animal. In other words, they figured out how to walk all over again, but in a way that works for them, using their winged forelimbs (or "arms") like a toad uses its hindlegs. This allows the winged parasites to approach large animals like cattle from a variety of angles, often while the victim is asleep.

If the prey is covered with feathers or fur, the vampire bat can clip hair away with shear-like canines. It then sinks its razor-sharp teeth into the skin and laps up blood with its tongue. Vampire bats can consume more than half their weight in blood within 20 minutes, Schutt says. But they don't take enough blood to kill an animal; 2 tablespoons is all they require. The digestive system immediately ramps up to break down the blood's protein and expel the excess water. Even so, they remain much heavier than before. But the bat's forelimb, which also powers its flight, can launch these blood-gorged animals skyward, generating a force almost 10 times their body weight. No other bat has such a powerful leap, Schutt says.

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Their Noses Are Amazing

Like most bats, vampires use sonar to help them find prey. But they also have a secret weapon shared only with certain types of snakes: the ability to sense heat from a distance. David Julius, a researcher at the University of California, San Francisco, published a study in Nature earlier this month showing these animals have cell receptors in their faces that help them aim their bites toward a warm area with lots of blood. It's the same type of cellular receptor humans have in their skin to sense painful heat. But in the vampire bat, these receptors can detect infrared radiation from up to 8 inches away. "These receptors allow the bats to find the area that is warmest, where the circulatory system is closest to the skin," Julius says. And while the receptors in human skin are sensitive only to heat above 109 F, the vampire bat's channels are more sensitive, detecting heat above 86 degrees.

Julius's team also compared the structure of the vampire bats' receptors with those of other animals. The results support recent evidence that bats are related to cows, dogs and moles, contrary to the prevailing idea that bats are descended from simpler, rodent-like ancestors. "It's consistent with more recent suggestions that bats are more closely related to placental mammals like dogs, horses, whales," Julius says.

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They're Social

Although they don't have Twitter, vampires have surprisingly complex social networks, establishing nuanced relationships like those between some primates. One reason for this might be their long life spans: Gerry Carter, a doctoral student at the University of Maryland who studies vampire bat societies, says the animals live up to 20 years in the wild, and females can spend nine months nursing their young. One of the vampires' favorite pastimes is grooming themselves and others, which strengthen social bonds and also keeps the animals free of parasites (perhaps ironic, since vampire bats are parasites themselves).

Plus, the vampire bat lifestyle demands cooperation. Relying upon blood as a food source comes with a high cost of failure—vampire bats will die if they don't eat for two or three nights. Perhaps for that reason, vampire bats share food with one another, regurgitating it into one another's mouths. Although this primarily occurs between females and their young, it also happens between unrelated animals. And bats keep score: Hungry bats that have received blood from a luckier neighbor are more likely to later return the favor if the same animal goes hungry. Greedy bats that don't share are more likely to starve if they cannot find their own meal, Carter says.

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They Could Be the Key to New Drugs

When a vampire bat bites its prey, special chemicals in its saliva keep the blood flowing. One of these, desmoteplase, has shown promise in humans as a treatment for stroke and other diseases. Danish pharmaceutical company Lundbeck will complete two phase-three studies (the final stage of drug development) of desmoteplase this year and next. If results are promising, they plan to release a drug to the public soon after, the company says.

Desmoteplase rapidly dissolves blood clots, and so the idea is to use it to target the clots that impede blood flow to the brain and cause a stroke. The only current treatment, a drug called tissue plasminogen activator, or TPA, can only be given within 3 hours of a stroke and carries the risk of causing internal bleeding. Lundbeck says that desmoteplase doesn't cause this dangerous side effect, and it could be effective up to 9 hours after a stroke.

Although vampires spread rabies, they also offer clues to its treatment. Less than one percent of wild vampires actually carry the virus, but many more test positive for rabies antibodies, Mistry says. "This means that a good number of bats in the wild are not rabid, but have been exposed to the virus, and their immune system has responded by creating antibodies, much as we might fight off the flu," he says. Such high survival rates for a disease that is deadly in humans raises interesting questions about how the bat immune system responds. This could lead to a better understanding of how to treat rabies in humans, Mistry says.

Vampire bats are frightening for obvious reasons: They can suck your blood, they fly around at night and can run on the ground, and they can spread rabies. But they prefer cattle to humans, and unless you're sleeping outside at night in vampire territory, you have little to fear. Perhaps they can even teach us a thing or two, Schutt says. Their specialized ability to sense heat could help humans better understand our own ability to detect heat and pain. The animal's reciprocity and altruism gives us hints about the development of this human-like trait in other animals. And maybe someday, bat-derived drugs such as desmoteplase could even save lives.

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